Hypothermia following whole-body heating of mice: Effect of heating time and temperature

Abstract

We have observed an acute and prolonged lowering of body temperature (hypothermia) following whole body heating (WBH) of mice. This phenomenon of heat-induced hypothermia and the subsequent recovery of normal temperatures have been systematically investigated. The hypothermic period can be characterized by two parameters: T_nadir and a recovery time constant (τ). For treatment temperatures below 41°C and treatment durations of 1 h or less, a mild hypothermia (T_nadir > 33°C) and fast recovery (τ < 1 h) occur. T_nadir and τ vary slightly with treatment temperature and are almost independent of treatment length. At treatment temperatures 41°C and above for up to 1 h, we observed acute hypothermia (T_nadir as low as 28°C) and slow recovery (τ = several hours). This region of prolonged hypothermia is characterized by a rapid change of T_nadir and τ with temperature, and a much less rapid change with treatment duration. The WBH temperature—time range causing prolonged hypothermia is very narrow, and if exceeded results in lethality. Critical lethal temperatures have been estimated for several treatment durations from the time constant data. Post-WBH hypothermia can be minimized by keeping the animals in a 37°C environment. However, we find that neither survivability nor intestinal cell repopulation is enhanced by this procedure.

Key Words:

• whole body hyperthermia
• hypothermia
• thermoregulation